Remove the need for a DATABASE_URL

Since the application does not use a database, it's confusing to have to
set a bogus database URL environment variable. This change follows [the
Lucky guide][1] suggestion for disabling the need for database
configuration. That makes the setup a little easier.

[1]:
https://www.luckyframework.org/guides/database/intro-to-avram-and-orms

script/docker_entrypoint

@@ -1,4 +1,4 @@
 #!/bin/sh
 
-echo -e "port: ${SCRIBE_PORT}\nhost: ${SCRIBE_HOST}\ndatabase: ${SCRIBE_DB}" > ./config/watch.yml
+echo -e "port: ${SCRIBE_PORT}\nhost: ${SCRIBE_HOST}" > ./config/watch.yml
 ./start_server